Hit points is the measurement unit for your life. It's indicated by circles in the upper left corner, where black circles indicate how many times the enemies have kicked your butt, and grey circles indicate how many more times they can do it before you lose your helmet or your life.
Losing a hit pointEdit
All enemy attacks that hit you will deplete one hit point. So will the spikes and Drill blocks that are found in many levels. However, other things will kill you instantly, regardless of how many Hit points you have left; broadly speaking, these are: Being crushed (by platforms, returning elevators, fake steel, evanescent blocks or by switching helmet in a place where there isn't enough room for you), falling off the bottom of the map or getting annihilated by prodding a murder wall. Diamond powers can't save you from an instant death, except Berzerker and Skycutters' invincibility power, which can keep you alive inside of a murder wall.
Gaining a hit pointEdit
The Kid's hit points will be restored whenever you pick up a helmet, and your hit point meter will be extended to the helmet's maximum hit points.
Number of hit pointsEdit
The Kid has two hit points - lose both and he'll die. All helmets have three hit points except for Iron Knight who has five. Lose all of a helmet's hitpoints and you'll revert back to the Kid with two more chances to not get killed.
Iron Knight can increase the number of total hit points you have. His second diamond power will add up to four extra hit points to your health at the cost of 50 diamonds per point, which will remain there even if you change helmets and progress through different stages. However, your extra hit points will NOT be retained if you die.